The following is an excerpt from my (co-written) book: Fundamentals of Chinese Medicine (PMPH press) 2015
Qi stagnation (qi zhì，气滞) is state of obstructed or stagnated qi flow in a particular part of the body. Qi stagnation can be associated with excess internal phlegm or dampness, food accumulation, blood stasis, heat constraint, zang-fu organ impairment or emotional depression. Any of these can impact the flow of qi and lead to a localized stagnation of qi movement that lead to functional disturbances of the zang-fu organs as well as the channels and collaterals. Qi stagnation is usually considered to be an excess-type pattern, although stagnation can result from patterns of deficient qi failing to move qi and blood. Manifestations of qi stagnation usually include distention, fullness and pain, chest distress, cough, and/or shortness of breath, as well as possible related signs of blood stasis or phlegm-fluid retention.
Qi stagnation has various clinical signs, but the most common characteristics simply involve a dull, achy discomfort. When qi stagnation combines with blood stasis, the result is a sharper pain, such as from over-exercise. (A very sharp pain such as from a bruise is attributed more to blood stasis alone, while a stabbing pain is often attributed to qi stagnation due to cold.)